SUBSCAPULARIS. ACTIONS OF SHOULDER MUSCLES. 203 



Mdatlonx. — Posteriorly this muscle is covered at its lower part by the latissimus 

 dorsi, and at its upper part it is crossed by the long head of the triceps. The 

 outer side is suiTounded obliquely by the latissimus dorsi : and the anterior 

 sm'face is concealed in the upper j^art of its extent by the tendon of that muscle. 

 The inner border of the muscle foi-ms the margin of a triangular space, of -nhich 

 the other sides are the upper part of the humerus, and the axillary border of the 

 scapula, covered before by the subscaptdar and behind by the teres minor muscles ; 

 this triangle is divided by the long head of the triceps into a superior or external 

 quadrilateral, and an inferior or internal, triangular compartment. Through the 

 quadrilatei-al space pass backwards the posterior circumflex vessels and the circum- 

 flex nerve ; and in the triangular subdivision the dorsal branch of the subsca- 

 pular artery passes round the margin of the scapula into the infraspinous fossa. 



Varietls.s: — The teres major muscle is sometimes found connected with the 

 fasciculi of the latissimus dorsi arising from the same part of the scapula. A 

 slip from this muscle has also been observed descending upon the fascia of the 

 upper arm extemallj'. 



The subscapularis muscle arises partly by muscular and partly by 

 tendinous fibres from the A'enter of the scapula, with the exception of 

 the neck of the bone and the spaces occupied by the serratus magnus ; 

 its fibres unite into a broad tendon which perforates the capsular liga- 

 ment of the shoulder-joint, and is inserted into the small tuberosity 

 of the humerus. Some fleshy fibres also are directly inserted into the 

 bone for a short distance lower down. Three or four tendinous 

 septa, attached to the ridges of the subscapular fossa, pass outwards in 

 the origin of the muscle ; and others are prolonged inwards from the 

 tendon of insertion. 



Brlations. — The tendon of the subscapulaiis is incorjiorated with the capsule 

 of the shoulder-joint, and between its upper and posterior surface, the coracoid 

 process, and the neck of the scapula is a bursa usually communicating with that 

 joint. There is also sometimes a bursa intei-vening between the anterior surface 

 of the muscle and the origin of the biceps and coraco-brachialis muscles. Ante- 

 riorly the muscle is in contact at its origin with the serratus mag-nus. and is 

 covered at its insertion by the coraco-brachialis and biceps, whUe, in the interval 

 between, it forms part of the posterior wall of the axilla. 



Variitics. — The varieties hitherto observed in this muscle are not considerable. 

 A small additional muscle, of somewhat variable form, has been described by 

 different authors, as passing from the surface of the subscapularis over the 

 capsular ligament, bvit without piercing it, to be inserted into or near the inner 

 margin of the bicipital groove, the xubf.capnlo-cajyuiilarix of Wenzel Gruber. 



Nerves of the Shoulder Muscles. — The supraspinatus and infraspinatus 

 muscles receive their nerves from the suprascapular branch which proceeds from 

 the upper loop of the brachial plexus, and therefore from the fifth and sixth 

 cervical nerves. The other muscles of this group are all supplied with nerves 

 from the posteiior division of the plexus, as follows : the deltoid and teres minor 

 from the circumflex nerve, the teres major and the subscapularis from the middle 

 and short subscapular nerves. 



Actions of the Shoulder Muscles. — The deltoid muscle raises the arm from 

 the side as far as the structure of the shoulder- joint permits, viz.. till it is at 

 right angles with the trunk. Firrther elevation of the upper limb is eft'ected chiefly 

 by the trapezius ; and it may be remarked that the insertion of that muscle cor- 

 responds exactly in extent to the origin of the deltoid, so that the two muscles may 

 be considered continuous in structure as well as in action. The anterior fibres of 

 the deltoid combine with the pectoralis major to draw the humerus fom^ards ; the 

 posterior assist in drawing it backwards. ITie supraspinatus. infraspinatus, and 

 subscapularis muscles being placed more closely round the joint, when acting in 

 concert with the deltoid, probably give steadiness and i)recision, while the deltoid 

 gives the main elevating force to the movement. The supraspinatus simply 

 elevates ; the infraspinatus and subscapularis carry the arm backwards or for- 



